Compounds related to assays

ABSTRACT

The present invention is generally directed to thiol quantitation assays, methods of performing the assays, and compounds used in the assays. It is more specifically directed to assays that include one or more disulfides and related molecules and methods. The disulfides contain a FRET pair.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/804,739, filed Jul. 28, 2010, which claims priority to U.S.Provisional Patent Application Ser. No. 61/273,186, filed on Jul. 30,2009, the entire disclosures of which are incorporated by reference.

FIELD OF THE INVENTION

The present invention is generally directed to thiol quantitationassays, methods of performing the assays, and compounds used in theassays. It is more specifically directed to assays that include one ormore disulfides and related molecules and methods.

BACKGROUND OF THE INVENTION

Thiols play a number of important roles in cellular biochemistry. Incertain cases they determine protein structure; in others they serve ascovalent catalysts; in still others they maintain appropriate oxidationstates of proteins and cells. Accordingly, thiol detection andquantitation is important to understanding cellular processes.

Several assays have been developed for thiol quantitation. One suchassay is the Thiol and Sulfide Quantitation Kit commercialized byInvitrogen. The kit includes the following: Papain-SSCH₃, adisulfide-inhibited papain derivative; L-BAPNA, a chromogenic papainsubstrate; DTNB (Ellman's reagent) for calibrating the assay; cystamine;L-cysteine, a thiol standard; and a buffer. According to productliterature, the chemical basis for the assay involves the followingreactions: 1) Papain-SSCH₃ is activated in the presence of thiols. 2)Active papain cleaves the substrate L-BAPNA, which releases thep-nitroaniline chromophore. 3) Protein thiols exchange with cystamine togenerate 2-mercaptoethylamine, which is detected.

Another thiol quantitation assay has been worked on at MarquetteUniversity by Sem and Pellela. See U.S. patent application Ser. No.11/512,465, issued as U.S. Pat. No. 7,820,833 on Oct. 26, 2010. Theirwork focuses on hydroxyl-coumarin-based disulfides, which reportedlyreact with sulfides present in the assay well. In a related publicationthe researches noted it was difficult to find a molecule that workedeffectively in an assay framework. See, The FASEB Journal, 2008;22:1049.3.

Despite the efforts discussed above, there is still a need for novelthiol quantitation assays that meet the unmet needs of variousresearchers.

SUMMARY OF THE INVENTION

The present invention is generally directed to thiol quantitationassays, methods of performing the assays, and compounds used in theassays. It is more specifically directed to assays that include one ormore disulfides and related molecules and methods.

In a method aspect, the present invention provides a method ofquantifying a thiol in a sample. The method comprises the steps of a)contacting the sample with a disulfide; and, b) detecting fluorescencefrom a cleavage product of the disulfide after the cleavage product hasbeen excited. The disulfide is of the following structure:

wherein R₁ is OH or NH₂, R₂ is H or SO₃—, R₃ is H or SO₃—, and R₄ isNH₂+ or O; and wherein X—Y is a symmetrical or unsymmetrical disulfidehaving the general structure —NH—R₅—SS—R₆—NH—, where R₅ and R₆ areeither aryl groups or alkyl groups.

In a compound aspect, the present invention provides a disulfide of thefollowing structure:

wherein R₁ is OH or NH₂, R₂ is H or SO₃—, R₃ is H or SO₃—, and R₄ isNH₂+ or O; and wherein X—Y is a symmetrical or unsymmetrical disulfidehaving the general structure —NH—R₅—SS—R₆—NH—, where R₅ and R₆ areeither aryl groups or alkyl groups.

DETAILED DESCRIPTION OF THE INVENTION

The present assays include one or more disulfide compounds. Thedisulfides contain a donor-acceptor FRET pair. When the disulfide isadded to an assay medium, thiols present in the medium cleave thedisulfide. This allows the emission spectrum of the donor portion of thepair to be observed; a thiol is detected and can be quantified accordingto the intensity of the emission.

Disulfides according to the present invention have a general structureas shown below (Structure I):

R₁ is OH or NH; R₂ is H or SO₃—; R₃ is H or SO₃—; and R₄ is O or NH₂+.“X—Y” is a symmetrical or unsymmetrical disulfide having the generalstructure —NH—R₅—SS—R₆—NH—, where R₅ and R₆ are either aryl groups oralkyl groups.

Structure II and Structure III below depict two more specific structuresof disulfides of the present invention, where the substitution patternon one aryl moiety is defined. The substituents for these structures arethe same as for Structure I.

Structure IV and Structure V below depict two still more specificstructures of disulfides of the present invention, where thesubstitution pattern on one aryl moiety and the tricyclic moiety aredefined. Substituents “X—Y” for these structures are the same as forStructure I.

As noted above, the group “X—Y” is a symmetrical or unsymmetricaldisulfide having the general structure —NH—R₅—SS—R₆—NH—, where R₅ and R₆are either aryl groups or alkyl groups. The aryl groups can beunsubstituted aryl groups, substituted aryl groups, unsubstitutedheteroaryl groups and substituted heteroaryl groups. An unsubstitutedaryl group is represented by Structure VI, Structure VII or StructureVIII below.

A substituted aryl group is represented by Structure IX, Structure X orStructure XI below.

R₇, R₈, R₉ and R₁₀ are independently selected from the group consistingof H, CH₃, CH₂CH₃, CH₂CH₂CH₃, CH(CH₃)₂, F, Cl, Br, I, CN, OCH₃, OCH₂CH₃,CO₂CH₃, CO₂CH₂CH₃, N(CH₃)₂, N(CH₂CH₃)₂, SCH₃, SCH₂CH₃; at least one ofthe substituents is not H.

An unsubstituted heteroaryl group is represented by Structure XII,Structure XIII, Structure XIV, Structure XV, Structure XVI, StructureXVII, Structure XVIII, Structure XIX and Structure XX below.

A substituted heteroaryl group is represented by Structure XXI,Structure XXII, Structure XXIII, Structure XXIV, Structure XXV,Structure XXVI, Structure XXVII, Structure XXVIII and Structure XXIXbelow.

R₁₁ and R₁₂ are independently selected from the group consisting of H,CH₃, CH₂CH₃, CH₂CH₂CH₃, CH(CH₃)₂, F, Cl, Br, I, CN, OCH₃, OCH₂CH₃,CO₂CH₃, CO₂CH₂CH₃, N(CH₃)₂, N(CH₂CH₃)₂, SCH₃, SCH₂CH₃; at least one ofthe substituents is not H.

R₁₃ and R₁₄ are independently selected from the group consisting of H,CH₃, CH₂CH₃, CH₂CH₂CH₃, CH(CH₃)₂, F, Cl, Br, I, CN, OCH₃, OCH₂CH₃,CO₂CH₃, CO₂CH₂CH₃, N(CH₃)₂, N(CH₂CH₃)₂, SCH₃, SCH₂CH₃; at least one ofthe substituents is not H.

R₁₅ and R₁₆ are independently selected from the group consisting of H,CH₃, CH₂CH₃, CH₂CH₂CH₃, CH(CH₃)₂, F, Cl, Br, I, CN, OCH₃, OCH₂CH₃,CO₂CH₃, CO₂CH₂CH₃, N(CH₃)₂, N(CH₂CH₃)₂, SCH₃, SCH₂CH₃; at least one ofthe substituents is not H.

Where R₅ and/or R₆ are alkyl groups, the alkyl groups can beunsubstituted alkyl groups, substituted alkyl groups and heteroalkylgroups. The following are non-limiting examples of unsubstituted alkylgroups: —CH₂CH₂—; —CH₂CH₂CH₂—; —CH(CH₃)CH₂—; —CH(CH₃)CH₂CH₂—;—CH₂CH(CH₃)CH₂—. The following are non-limiting examples of substitutedalkyl groups: —CH(CO₂CH₃)CH₂—; —CH(CO₂CH₂CH₃)CH₂—; —CH₂CH(OCH₃)CH₂—;—CH₂CH(CN)CH₂—; —CH₂CH(CO₂CH₃)CH₂—; —CH₂CH(CH₂CO₂CH₃)CH₂—;—CH₂CH(OCH₃)CH₂CH₂—. The following are non-limiting examples ofheteroalkyl groups: —CH₂CH₂—O—CH₂CH₂—; —CH₂CH₂—N[C(O)CH₃]—CH₂CH₂—;—CH₂CH₂—S—CH₂CH₂—.

The group “X—Y” is symmetrical or asymmetrical. Non-limiting examples ofsuch groups are: —NH—CH₂CH₂—SS—CH₂CH₂—NH—; —NH—(C₆H₄)—SS—(C₆H₄)—NH—;—NH—CH₂CH₂—SS—(C₆H₄)—NH—; —NH—(C₆H₄)—SS—CH₂CH₂—NH—;—NH—CH₂CH₂—SS—CH₂CH₂CH₂—NH—; —NH—CH₂CH₂CH₂—SS—CH₂CH₂—NH—;—NH—CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—; —NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—; —NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂CH₂CH₂—NH—;—NH—CH₂CH₂—OCH₂CH₂—SS—CH₂CH₂—NH—; —NH—CH₂CH₂OCH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂OCH₂CH₂—SS—CH₂CH₂CH₂CH₂—NH—;—NH—CH₂CH₂OCH₂CH₂—SS—CH₂CH₂OCH₂CH₂—NH—; —NH—CH₂CH₂—SS—CH₂CH₂OCH₂CH₂—NH—;—NHCH₂CH₂CH₂—SS—CH₂CH₂OCH₂CH₂NH—; —NHCH₂CH₂CH₂CH₂—SS—CH₂CH₂OCH₂CH₂NH—;—NH—CH₂CH₂—SS—(C₄H₂O)—NH—; —NH—CH₂CH₂CH₂—SS—(C₄H₂O)—NH—;—NH—CH₂CH₂CH₂CH₂—SS—(C₄H₂O)—NH—; —NH—CH₂CH₂OCH₂CH₂—SS—(C₄H₂O)—NH—;—NH—(C₄H₂O)—SS—CH₂CH₂—NH—; —NH—(C₄H₂O)—SS—CH₂CH₂CH₂—NH—;—NH—(C₄H₂O)—SS—CH₂CH₂CH₂CH₂—NH—; —NH—(C₄H₂O)—SS—CH₂CH₂OCH₂CH₂—NH—;—NH(C₄H₂O)—SS—(C₄H₂O)—NH—; —NH—CH₂CH₂—SS—(C₄H₂S)—NH—;—NH—CH₂CH₂CH₂—SS—(C₄H₂S)—NH—; —NH—CH₂CH₂CH₂CH₂—SS—(C₄H₂S)—NH—;—NH—CH₂CH₂OCH₂CH₂—SS—(C₄H₂S)—NH—; —NH—(C₄H₂S)—SS—CH₂CH₂—NH—;—NH—(C₄H₂S)—SS—CH₂CH₂CH₂—NH—; —NH—(C₄H₂S)—SS—CH₂CH₂CH₂CH₂—NH—;—NH—(C₄H₂S)—SS—CH₂CH₂OCH₂CH₂—NH—; —NH(C₄H₂S)—SS—(C₄H₂S)—NH—.

Referring to Structure II, the following are non-limiting examples ofdisulfides according to the present invention:

Example 1

R₁ is NH₂; R₂ is SO₃—; R₃ is SO₃—; R₄ is NH₂+; X—Y is—NH—CH₂CH₂—SS—CH₂CH₂—NH—.

Example 2

R₁ is NH₂; R₂ is SO₃—; R₃ is SO₃—; R₄ is NH₂+; X—Y is—NH—(pC₆H₄)—SS—(pC₆H₄)—NH—.

Example 3

R₁ is NH₂; R₂ is SO₃—; R₃ is SO₃—; R₄ is NH₂+; X—Y is—NH—CH₂CH₂—SS—CH₂CH₂CH₂—NH—.

Example 4

R₁ is NH₂; R₂ is SO₃—; R₃ is SO₃—; R₄ is NH₂+; X—Y is—NH—CH₂CH₂CH₂—SS—CH₂CH₂—NH—.

Example 5

R₁ is NH₂; R₂ is SO₃—; R₃ is SO₃—; R₄ is NH₂+; X—Y is—NH—CH₂CH₂—SS—(pC₆H₄)—NH—.

Example 6

R₁ is NH₂; R₂ is SO₃—; R₃ is SO₃—; R₄ is NH₂+; X—Y is—NH—(pC₆H₄)—SS—CH₂CH₂—NH—.

Example 7

R₁ is OH; R₂ is H; R₃ is H; R₄ is O; XY is —NHCH₂CH₂—SS—CH₂CH₂—NH—.

Example 8

R₁ is OH; R₂ is H; R₃ is H; R₄ is O; XY is —NH—(pC₆H₄)—SS—(pC₆H₄)—NH—.

Example 9

R₁ is OH; R₂ is H; R₃ is H; R₄ is O; XY is —NH—CH₂CH₂—SS—CH₂CH₂CH₂—NH—.

Example 10

R₁ is OH; R₂ is H; R₃ is H; R₄ is O; XY is —NH—CH₂CH₂CH₂—SS—CH₂CH₂—NH—.

Example 11

R₁ is OH; R₂ is H; R₃ is H; R₄ is O; XY is —NH—CH₂CH₂—SS—(pC₆H₄)—NH—.

Example 12

R₁ is OH; R₂ is H; R₃ is H; R₄ is O; XY is —NH—(pC₆H₄)—SS—CH₂CH₂—NH—.

Referring to Structure III, the following are non-limiting examples ofdisulfides according to the present invention:

Example 13

R₁ is NH₂; R₂ is SO₃—; R₃ is SO₃—; R₄ is NH₂+; X—Y is—NH—CH₂CH₂—SS—CH₂CH₂—NH—.

Example 14

R₁ is NH₂; R₂ is SO₃—; R₃ is SO₃—; R₄ is NH₂+; X—Y is—NH—(pC₆H₄)—SS—(pC₆H₄)—NH—.

Example 15

R₁ is NH₂; R₂ is SO₃—; R₃ is SO₃—; R₄ is NH₂+; X—Y is—NH—CH₂CH₂—SS—CH₂CH₂CH₂—NH—.

Example 16

R₁ is NH₂; R₂ is SO₃—; R₃ is SO₃—; R₄ is NH₂+; X—Y is—NH—CH₂CH₂CH₂—SS—CH₂CH₂—NH—.

Example 17

R₁ is NH₂; R₂ is SO₃—; R₃ is SO₃—; R₄ is NH₂+; X—Y is—NH—CH₂CH₂—SS—(pC₆H₄)—NH—.

Example 18

R₁ is NH₂; R₂ is SO₃—; R₃ is SO₃—; R₄ is NH₂+; X—Y is—NH—(pC₆H₄)—SS—CH₂CH₂—NH—.

Example 19

R₁ is OH; R₂ is H; R₃ is H; R₄ is O; XY is —NHCH₂CH₂—SS—CH₂CH₂—NH—.

Example 20

R₁ is OH; R₂ is H; R₃ is H; R₄ is O; XY is —NH—(pC₆H₄)—SS—(pC₆H₄)—NH—.

Example 21

R₁ is OH; R₂ is H; R₃ is H; R₄ is O; XY is —NH—CH₂CH₂—SS—CH₂CH₂CH₂—NH—.

Example 22

R₁ is OH; R₂ is H; R₃ is H; R₄ is O; XY is —NH—CH₂CH₂CH₂—SS—CH₂CH₂—NH—.

Example 23

R₁ is OH; R₂ is H; R₃ is H; R₄ is O; XY is —NH—CH₂CH₂—SS—(pC₆H₄)—NH—.

Example 24

R₁ is OH; R₂ is H; R₃ is H; R₄ is O; XY is —NH—(pC₆H₄)—SS—CH₂CH₂—NH—.

The disulfides of the present invention are synthesized according tomethods known to those skilled in the art. Examples of reaction typesthat are used to synthesize the disulfides can be found in U.S. patentapplication Ser. No. 11/512,485, issued as U.S. Pat. No. 7,820,833 onOct. 26, 2010, which is incorporated-by-reference into this document forall purposes. One such reaction type is a condensation of a diamine(e.g., H₂N—CH₂CH₂—SS—CH₂CH₂NH₂ and H₂N—(C₆H₄)—SS—(C₆H₄)—NH₂) with anactivated carboxylic acid moiety of a FRET pair donor and a FRET pairacceptor, which is typically performed in two separate synthetic steps.

Assays of the present invention are performed by bringing a disulfide ofthe present invention in contact with a sample thought to include one ormore types of thiols. As noted above, the disulfides contain adonor-acceptor FRET pair. When the disulfide is added to the sample,thiols present in the sample cleave the disulfide. Cleavage ensures thatthe acceptor no longer quenches the emission spectrum of the donorportion of the FRET pair. Excitation of the donor accordingly results influorescence, which can be measured.

The invention claimed is:
 1. A compound, wherein the compound is of thefollowing structure:

wherein X—Y is a symmetrical or unsymmetrical disulfide selected fromthe following group of disulfides: —NH—CH₂CH₂—SS—CH₂CH₂NH—;—NH—(C₆H₄)—SS—(C₆H₄)—NH—; —NH—CH₂CH₂—SS—(C₆H₄)—NH—;—NH—(C₆H₄)—SS—CH₂CH₂—NH—; —NH—CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂—SS—CH₂CH₂—NH—; —NH—CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂—NH—; —NHCH₂CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂CH₂CH₂—NH—; —NH—CH₂CH₂OCH₂CH₂—SS—CH₂CH₂—NH—;—NH—CH₂CH₂OCH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂OCH₂CH₂—SS—CH₂CH₂CH₂CH₂—NH—;—NH—CH₂CH₂OCH₂CH₂—SS—CH₂CH₂OCH₂CH₂—NH—; —NH—CH₂CH₂—SS—CH₂CH₂OCH₂CH₂—NH;—NH—CH₂CH₂CH₂—SS—CH₂CH₂OCH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂OCH₂CH₂—NH—; —NH—CH₂CH₂—SS—(C₄H₂O)—NH—;—NH—CH₂CH₂CH₂—SS—(C₄H₂O)—NH—; —NH—CH₂CH₂CH₂CH₂—SS—(C₄H₂O)—NH—;—NH—CH₂CH₂OCH₂CH₂—SS—(C₄H₂O)—NH—; —NH—(C₄H₂O)—SS—CH₂CH₂—NH—;—NH—(C₄H₂O)—SS—CH₂CH₂CH₂—NH—; —NH—(C₄H₂O)—SS—CH₂CH₂CH₂CH₂—NH—;—NH—(C₄H₂O)—SS—CH₂CH₂OCH₂CH₂—NH—; —NH—(C₄H₂O)—SS—(C₄H₂O)—NH—;—NH—CH₂CH₂—SS—(C₄H₂S)—NH—; —NH—CH₂CH₂CH₂—SS—(C₄H₂S)—NH—;—NH—CH₂CH₂CH₂CH₂—SS—(C₄H₂S)—NH—; —NH—CH₂CH₂OCH₂CH₂—SS—(C₄H₂S)—NH—;—NH—(C₄H₂S)—SS—CH₂CH₂—NH—; —NH—(C₄H₂S)—SS—CH₂CH₂CH₂—NH—;—NH—(C₄H₂S)—SS—CH₂CH₂CH₂CH₂—NH—; —NH—(C₄H₂S)—SS—CH₂CH₂OCH₂CH₂—NH—;—NH—(C₄H₂S)—SS—(C₄H₂S)—NH—.
 2. The compound according to claim 1,wherein X—Y is a symmetrical or unsymmetrical disulfide selected fromthe following group of disulfides: —NH—CH₂CH₂—SS—CH₂CH₂NH—;—NH—(C₆H₄)—SS—(C₆H₄)—NH—; —NH—CH₂CH₂—SS—(C₆H₄)—NH—;—NH—(C₆H₄)—SS—CH₂CH₂—NH—; —NH—CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂—SS—CH₂CH₂—NH—; —NH—CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂—NH—; —NHCH₂CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂CH₂CH₂—NH—.
 3. The compound according to claim2, wherein X—Y is a symmetrical or unsymmetrical disulfide selected fromthe following group of disulfides: —NH—CH₂CH₂—SS—CH₂CH₂NH—;—NH—(C₆H₄)—SS—(C₆H₄)—NH—; —NH—CH₂CH₂—SS—(C₆H₄)—NH—;—NH—(C₆H₄)—SS—CH₂CH₂—NH—; —NH—CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂—SS—CH₂CH₂—NH—; —NH—CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—.
 4. Acompound, wherein the compound is of the following structure:

wherein X—Y is a symmetrical or unsymmetrical disulfide selected fromthe following group of disulfides: —NH—CH₂CH₂—SS—CH₂CH₂NH—;—NH—(C₆H₄)—SS—(C₆H₄)—NH—; —NH—CH₂CH₂—SS—(C₆H₄)—NH—;—NH—(C₆H₄)—SS—CH₂CH₂—NH—; —NH—CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂—SS—CH₂CH₂—NH—; —NH—CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂—NH—; —NHCH₂CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂CH₂CH₂—NH—; —NH—CH₂CH₂OCH₂CH₂—SS—CH₂CH₂—NH—;—NH—CH₂CH₂OCH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂OCH₂CH₂—SS—CH₂CH₂CH₂CH₂—NH—;—NH—CH₂CH₂OCH₂CH₂—SS—CH₂CH₂OCH₂CH₂—NH—; —NH—CH₂CH₂—SS—CH₂CH₂OCH₂CH₂—NH;—NH—CH₂CH₂CH₂—SS—CH₂CH₂OCH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂OCH₂CH₂—NH—; —NH—CH₂CH₂—SS—(C₄H₂O)—NH—;—NH—CH₂CH₂CH₂—SS—(C₄H₂O)—NH—; —NH—CH₂CH₂CH₂CH₂—SS—(C₄H₂O)—NH—;—NH—CH₂CH₂OCH₂CH₂—SS—(C₄H₂O)—NH—; —NH—(C₄H₂O)—SS—CH₂CH₂—NH—;—NH—(C₄H₂O)—SS—CH₂CH₂CH₂—NH—; —NH—(C₄H₂O)—SS—CH₂CH₂CH₂CH₂—NH—;—NH—(C₄H₂O)—SS—CH₂CH₂OCH₂CH₂—NH—; —NH—(C₄H₂O)—SS—(C₄H₂O)—NH—;—NH—CH₂CH₂—SS—(C₄H₂S)—NH—; —NH—CH₂CH₂CH₂—SS—(C₄H₂S)—NH—;—NH—CH₂CH₂CH₂CH₂—SS—(C₄H₂S)—NH—; —NH—CH₂CH₂OCH₂CH₂—SS—(C₄H₂S)—NH—;—NH—(C₄H₂S)—SS—CH₂CH₂—NH—; —NH—(C₄H₂S)—SS—CH₂CH₂CH₂—NH—;—NH—(C₄H₂S)—SS—CH₂CH₂CH₂CH₂—NH—; —NH—(C₄H₂S)—SS—CH₂CH₂OCH₂CH₂—NH—;—NH—(C₄H₂S)—SS—(C₄H₂S)—NH—.
 5. The compound according to claim 4,wherein X—Y is a symmetrical or unsymmetrical disulfide selected fromthe following group of disulfides: —NH—CH₂CH₂—SS—CH₂CH₂NH—;—NH—(C₆H₄)—SS—(C₆H₄)—NH—; —NH—CH₂CH₂—SS—(C₆H₄)—NH—;—NH—(C₆H₄)—SS—CH₂CH₂—NH—; —NH—CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂—SS—CH₂CH₂—NH—; —NH—CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂—NH—; —NHCH₂CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂CH₂CH₂—NH—.
 6. The compound according to claim5, wherein X—Y is a symmetrical or unsymmetrical disulfide selected fromthe following group of disulfides: —NH—CH₂CH₂—SS—CH₂CH₂NH—;—NH—(C₆H₄)—SS—(C₆H₄)—NH—; —NH—CH₂CH₂—SS—(C₆H₄)—NH—;—NH—(C₆H₄)—SS—CH₂CH₂—NH—; —NH—CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂—SS—CH₂CH₂—NH—; —NH—CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—.
 7. Acompound, wherein the compound is of the following structure:

wherein X—Y is a symmetrical or unsymmetrical disulfide selected fromthe following group of disulfides: —NH—CH₂CH₂—SS—CH₂CH₂NH—;—NH—(C₆H₄)—SS—(C₆H₄)—NH—; —NH—CH₂CH₂—SS—(C₆H₄)—NH—;—NH—(C₆H₄)—SS—CH₂CH₂—NH—; —NH—CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂—SS—CH₂CH₂—NH—; —NH—CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂—NH—; —NHCH₂CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂CH₂CH₂—NH—; —NH—CH₂CH₂OCH₂CH₂—SS—CH₂CH₂—NH—;—NH—CH₂CH₂OCH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂OCH₂CH₂—SS—CH₂CH₂CH₂CH₂—NH—;—NH—CH₂CH₂OCH₂CH₂—SS—CH₂CH₂OCH₂CH₂—NH—; —NH—CH₂CH₂—SS—CH₂CH₂OCH₂CH₂—NH;—NH—CH₂CH₂CH₂—SS—CH₂CH₂OCH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂OCH₂CH₂—NH—; —NH—CH₂CH₂—SS—(C₄H₂O)—NH—;—NH—CH₂CH₂CH₂—SS—(C₄H₂O)—NH—; —NH—CH₂CH₂CH₂CH₂—SS—(C₄H₂O)—NH—;—NH—CH₂CH₂OCH₂CH₂—SS—(C₄H₂O)—NH—; —NH—(C₄H₂O)—SS—CH₂CH₂—NH—;—NH—(C₄H₂O)—SS—CH₂CH₂CH₂—NH—; —NH—(C₄H₂O)—SS—CH₂CH₂CH₂CH₂—NH—;—NH—(C₄H₂O)—SS—CH₂CH₂OCH₂CH₂—NH—; —NH—(C₄H₂O)—SS—(C₄H₂O)—NH—;—NH—CH₂CH₂—SS—(C₄H₂S)—NH—; —NH—CH₂CH₂CH₂—SS—(C₄H₂S)—NH—;—NH—CH₂CH₂CH₂CH₂—SS—(C₄H₂S)—NH—; —NH—CH₂CH₂OCH₂CH₂—SS—(C₄H₂S)—NH—;—NH—(C₄H₂S)—SS—CH₂CH₂—NH—; —NH—(C₄H₂S)—SS—CH₂CH₂CH₂—NH—;—NH—(C₄H₂S)—SS—CH₂CH₂CH₂CH₂—NH—; —NH—(C₄H₂S)—SS—CH₂CH₂OCH₂CH₂—NH—;—NH—(C₄H₂S)—SS—(C₄H₂S)—NH—.
 8. The compound according to claim 7,wherein X—Y is a symmetrical or unsymmetrical disulfide selected fromthe following group of disulfides: —NH—CH₂CH₂—SS—CH₂CH₂NH—;—NH—(C₆H₄)—SS—(C₆H₄)—NH—; —NH—CH₂CH₂—SS—(C₆H₄)—NH—;—NH—(C₆H₄)—SS—CH₂CH₂—NH—; —NH—CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂—SS—CH₂CH₂—NH—; —NH—CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂—NH—; —NHCH₂CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂CH₂—SS—CH₂CH₂CH₂CH₂—NH—.
 9. The compound according to claim8, wherein X—Y is a symmetrical or unsymmetrical disulfide selected fromthe following group of disulfides: —NH—CH₂CH₂—SS—CH₂CH₂NH—;—NH—(C₆H₄)—SS—(C₆H₄)—NH—; —NH—CH₂CH₂—SS—(C₆H₄)—NH—;—NH—(C₆H₄)—SS—CH₂CH₂—NH—; —NH—CH₂CH₂—SS—CH₂CH₂CH₂—NH—;—NH—CH₂CH₂CH₂—SS—CH₂CH₂—NH—; —NH—CH₂CH₂CH₂—SS—CH₂CH₂CH₂—NH—.